The present invention relates to contrast agent imaging. In particular, a transmit power level is provided for contrast agent ultrasound imaging.
Contrast agents are typically gas or fluid filled micro-spheres which resonate at ultrasound frequencies. The contrast agents are injected into the blood stream and carried to various locations in the body. When insonified, echo signals are generated due to resonance of the contrast agents. The echo signals provide good contrast to signals from the surrounding tissue or fluid.
Destruction of contrast agents prevents repetitive scanning or real-time imaging. At higher powers, pressures, or mechanical indices (MI), the micro-spheres can burst and be eliminated from a scanning plane. Since contrast agents can move slowly through the body's vasculature, the microspheres do not quickly enter the imaged tissue. With high MI imaging, slower scanning rates are required to allow fresh agent to replenish the scanning plane.
Contrast agents are imaged with low MI or low transmitted power levels to avoid destruction. High frame rates for imaging can be maintained. For low MI imaging, the user selects a transmit power or the system uses a pre-set contrast agent imaging transmit power. Unlike tissue imaging or imaging of contrast agents at high MI, low MI imaging of contrast agents can be more challenging. Returned signals can be weak, and a user may often search for a preferred transmit power level. The user subjectively determines a transmit power level that minimizes bubble destruction but maintains a sufficient signal-to-noise ratio. This takes time and training. Systems that fix, or preset, the transmitted power levels for an examination can improve the efficiency of an examination. However, the preset values may not be optimal. Preset values may be sub-optimal due to different patient types, different clinical applications, or different contrast agents.